US20190161838A1

US20190161838A1 - High-strength bainitic steel

Info

Publication number: US20190161838A1
Application number: US15/824,704
Authority: US
Inventors: Jianghuai Yang; Qigui Wang; Daniel J Wilson; James D Cremonesi
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2017-11-28
Filing date: 2017-11-28
Publication date: 2019-05-30
Also published as: DE102018129828A1; CN109837458A

Abstract

A high-strength steel alloy and automotive components produced therefrom, as well as a method for forming a steel alloy, are provided. The high-strength steel alloy includes iron, about 0.24 to about 0.80 weight percent carbon, about 0.40 to about 2.10 weight percent manganese, about 0.20 to about 1.60 weight percent silicon, about 0.05 to about 0.14 weight percent sulfur; about 0.10 to about 12.0 weight percent chromium, about 0.10 to about 2.50 weight percent nickel, and about 0.02 to about 0.07 weight percent aluminum. The steel alloy may also include boron, molybdenum, titanium, niobium, and/or nitrogen. The method includes air quenching a steel alloy component after mold shakeout until the component reaches a temperature in the range of 420 to 530 degrees Celsius.

Description

FIELD

The present disclosure relates generally to steel alloys, and more particularly, to high-strength steel alloys and casting processes for forming them, as well as components made therefrom, such as crankshafts.

INTRODUCTION

An engine's crankshaft converts reciprocating linear movement of a piston into rotational movement about a crank axis to provide torque to propel a vehicle, such as but not limited to a train, a boat, a plane, or an automobile. Crankshafts are a vital part of an engine, and are a starting point of engine design. Crankshaft design affects the overall packaging of the engine, and thereby the total mass of the engine. Accordingly, minimizing the size and/or mass of the crankshaft reduces the size and mass of the engine, which has a compounding effect on the overall size, mass and fuel economy of the vehicle.
The crankshaft includes at least one crank pin journal that is offset from the crank axis, to which a reciprocating piston is attached via a connecting rod. Force applied from the piston to the crankshaft through the offset connection therebetween generates torque in the crankshaft, which rotates the crankshaft about the crank axis. The crankshaft further includes at least one main bearing journal disposed concentrically about the crank axis. The crankshaft is secured to an engine block at the main bearing journals. A bearing is disposed about the main bearing journal, between the crankshaft and the engine block.
The crankshaft may be formed or manufactured by a casting process, such as but not limited to a green sand casting process or a shell mold casting process, which uses cast iron to form the crankshaft. Alternatively, the crankshaft may be forged from a steel alloy. Steel is stronger than cast iron, and therefore is a more desirable material to use for crankshafts. Although the forging process is more costly than the casting process, most steel alloys exhibit a high shrinkage while cooling, and do not cast well, because the shrinkage that occurs while the cast product cools forms voids in the final cast product. This weakens the final cast product and makes it unsuitable for use in an engine.

SUMMARY

This disclosure provides a high-strength steel alloy that is suitable for use in casting a crankshaft. The steel alloy features a medium-low carbon content for sufficiently high hardenability, fine grain sizes, a microstructure featuring a substantial amount of bainite, and with good machinability. The final microstructure may consist largely of lower bainite and/or upper bainite, and as such, subsequent heat treating can be eliminated, if desired. An ultimate tensile strength in the range of 750 to 1100 MPa can be obtained.
The disclosed steel alloy contains iron, carbon, manganese, silicon, sulfur, chromium, nickel, molybdenum, and aluminum. In some forms, boron, vanadium, nitrogen, titanium, and/or niobium may also be included.
In one example, which may be combined with or separate from the other examples and features provided herein, a high-strength steel alloy is provided containing: iron, about 0.24 to about 0.80 weight percent carbon, about 0.40 to about 2.10 weight percent manganese, about 0.20 to about 1.60 weight percent silicon, about 0.05 to about 0.14 weight percent sulfur, about 0.10 to about 12.0 weight percent chromium, about 0.10 to about 2.50 weight percent nickel, and about 0.02 to about 0.07 weight percent aluminum.
In another example, which may be combined with or separate from the other examples and features provided herein, a high-strength steel alloy is provided that consists essentially of: about 0.35 weight percent carbon, about 1.65 weight percent manganese, about 0.45 weight percent silicon, about 0.4 weight percent chromium, about 0.7 weight percent nickel, about 0.25 weight percent molybdenum, and the balance iron.
In yet another example, which may be combined with or separate from the other examples provided herein, a method of forming a steel alloy component is provided. The method includes creating a steel alloy comprising: iron, about 0.24 to about 0.80 weight percent carbon, about 0.40 to about 2.10 weight percent manganese, about 0.20 to about 1.60 weight percent silicon, about 0.05 to about 0.14 weight percent sulfur, about 0.10 to about 12.0 weight percent chromium, about 0.10 to about 2.50 weight percent nickel, and about 0.02 to about 0.07 weight percent aluminum. The method further includes casting in a mold the steel alloy to form the component. The method includes shaking out the mold and air quenching the component until the component has a temperature in the range of 420 to 530 degrees Celsius.
Further additional features may be provided, including but not limited to the following: the high-strength steel alloy further comprising boron in an amount not exceeding 0.005 weight percent; wherein the iron is provided in an amount between about 75.0 and about 98.88 weight percent; the high-strength steel alloy further comprising vanadium in an amount not exceeding 0.20 weight percent; the high-strength steel alloy further comprising molybdenum in an amount not exceeding 0.60 weight percent; the high-strength steel alloy further comprising titanium in an amount not exceeding 0.20 weight percent; the high-strength steel alloy further comprising niobium in an amount not exceeding 0.20 weight percent; the high-strength steel alloy further comprising about 0.001 to about 0.005 weight percent nitrogen; and/or the high-strength steel alloy further comprising about 0.01 to about 0.04 weight percent nitrogen.
In still another variation, the high-strength steel alloy comprises: about 0.24 to about 0.40 weight percent carbon, about 1.50 to about 2.00 weight percent manganese, about 0.40 to about 0.80 weight percent silicon, about 0.05 to about 0.12 weight percent sulfur, about 0.10 to about 0.60 weight percent chromium, about 0.60 to about 0.90 weight percent nickel, about 0.20 to about 0.40 weight percent molybdenum, about 0.02 to about 0.04 weight percent aluminum, and about 0.001 to about 0.005 weight percent boron.
In still another variation, the high-strength steel alloy comprises: about 0.25 to about 0.50 weight percent carbon, about 1.50 to about 2.00 weight percent manganese, about 0.30 to about 0.60 weight percent silicon, about 0.05 to about 0.12 weight percent sulfur, about 0.20 to about 0.60 weight percent chromium, about 0.50 to about 0.90 weight percent nickel, about 0.15 to about 0.40 weight percent molybdenum, about 0.02 to about 0.04 weight percent aluminum, and about 0.001 to about 0.005 weight percent boron.
A crankshaft for an automotive propulsion system is provided, which may be created from any of the variations of the high-strength steel alloy provided herein.
Other additional features may include, but are not limited to: the high-strength steel alloy having an ultimate tensile strength in the range of 750 to 1100 MPa; the high-strength steel alloy having an ASTM grain size number in the range of 5 to 8; the method further comprising holding the component at an isothermal temperature in the range of 420 to 530 Celsius starting immediately after the step of air quenching and continuing for a time period in the range of 1.5 to 3.5 hours; wherein the step of holding the component at the isothermal temperature is performed immediately after the step of air quenching without cooling the component to a temperature below 420 degrees Celsius between the step of air quenching and the step of holding the component at the isothermal temperature; and wherein the step of creating the steel alloy further comprises creating the steel alloy comprising boron in an amount not exceeding 0.005 weight percent.
Further aspects, advantages and areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings are provided for illustration purposes only and are not intended to limit this disclosure or the claims appended hereto.

FIG. 1 is a graph showing a conceptual time-temperature-transformation featured diagram of a steel alloy according to the principles of the present disclosure;

FIG. 2 is a graph showing a temperature-time diagram for a cooling process for forming high-strength steel alloys in accordance with the principles of the present disclosure;

FIG. 3 is a block diagram illustrating a method of forming a steel alloy component, according to the principles of the present disclosure;

FIG. 4A is a perspective view of a crankshaft formed of a steel alloy in accordance with the principles of the present disclosure; and

FIG. 4B is a cross-sectional view of the crankshaft of FIG. 4A, according to the principles of the present disclosure.

DETAILED DESCRIPTION

High strength steel alloys having a substantially bainite microstructure are provided. In comparison to other steel alloys, these steel alloys exhibit improved material strength and hardness, with relatively fine grain size and adequate ductility, as well as desirable castability and machinability. The steel alloys disclosed herein are useful for forming automotive components that undergo large loads and fatigue, such as crankshafts.
These steel alloys have a low to medium carbon content for sufficiently high hardenability, fine grain sizes, favorable bainitic microstructure, and ease of machining. The final microstructure consists primarily of lower to upper bainite, which can be achieved through a cooling process that eliminates the need for subsequent heat treatment, as will be described in further detail below. An ultimate tensile strength in the range of 750 to 1150 MPa with an elongation greater than 8% can be obtained. The disclosed steel alloys have equivalent Young's moduli to forged steel counterparts with better machinability. The steel alloy may be used in gas or diesel engine components, such as crankshafts, by way of example.
The steel alloys disclosed herein contain iron, carbon, manganese, silicon, sulfur, chromium, nickel, and aluminum. In some versions, boron, molybdenum, vanadium, nitrogen, titanium, and/or niobium may also be included.
The steel alloys disclosed herein may be high-strength steel alloys and may include iron and by weight about 0.24 to about 0.80 weight percent carbon; about 0.40 to about 2.10 weight percent manganese; about 0.20 to about 1.60 weight percent silicon; about 0.05 to about 0.14 weight percent sulfur; about 0.10 to about 12.0 weight percent chromium; about 0.10 to about 2.50 weight percent nickel; and about 0.02 to about 0.07 weight percent aluminum. For example, Table 1 shows this first example of the steel alloy, which contains iron, carbon, manganese, silicon, sulfur, chromium, nickel, and aluminum.

TABLE 1

Example of a New Steel Alloy

C	Mn	Si	S	Cr	Ni	Al
(wt %)	(wt %)	(wt %)	(wt %)	(wt %)	(wt %)	(wt %)	Fe

0.24-0.80	0.40-2.10	0.20-1.60	0.05-0.14	0.10-12.0	0.10-2.50	0.02-0.07	Balance
							or at least
							75 wt %

Further, in some variations, the steel alloy may include boron, molybdenum, vanadium, nitrogen, titanium, and/or niobum as follows: 0.0004-0.005 weight percent boron, 0.10-0.60 weight percent molybdenum, 0.05-0.20 weight percent vanadium, 0.02-0.20 weight percent titanium, 0.03-0.20 weight percent niobium, and 0.01-0.04 weight percent nitrogen. Thus, Table 2 shows the additional elements that may be added to the elements in Table 1 to form a new steel alloy as disclosed herein.

TABLE 2

Additional elements to optionally be added
to the steel alloy shown in Table 1.

B	Mo	V	Ti	Nb	N
(wt %)	(wt %)	(wt %)	(wt %)	(wt %)	(wt %)

0.0004-0.005	0.10-0.60	0.05-0.20	0.02-0.20	0.03-0.20	0.01-0.04

In some variations, the ranges of the steel alloy may be further refined to include iron and by weight about 0.24 to about 0.40 weight percent carbon; about 1.50 to about 2.00 weight percent manganese; about 0.40 to about 0.80 weight percent silicon; about 0.05 to about 0.12 weight percent sulfur; about 0.10 to about 0.60 weight percent chromium; about 0.60 to about 0.90 weight percent nickel; about 0.20 to about 0.40 weight percent molybdenum; about 0.02 to about 0.04 weight percent aluminum; and about 0.001 to about 0.005 weight percent boron. For example, Table 3 shows this example of the steel alloy, which contains these elements: iron, carbon, manganese, silicon, sulfur, chromium, nickel, molybdenum, aluminum, and boron.

TABLE 3

Example of a New Steel Alloy

C	Mn	Si	S	Cr	Ni	Mo	Al	B
(wt %)	(wt %)	(wt %)	(wt %)	(wt %)	(wt %)	(wt %)	(wt %)	(wt %)

0.24-0.40	1.50-2.00	0.40-0.80	0.05-0.12	0.10-0.60	0.60-0.90	0.20-0.40	0.02-0.04	0.001-0.005

In another variation, the ranges of the steel alloy may include iron and by weight about 0.25 to about 0.50 weight percent carbon; about 1.50 to about 2.00 weight percent manganese; about 0.30 to about 0.60 weight percent silicon; about 0.05 to about 0.12 weight percent sulfur; about 0.20 to about 0.60 weight percent chromium; about 0.50 to about 0.90 weight percent nickel; about 0.15 to about 0.40 weight percent molybdenum; about 0.02 to about 0.04 weight percent aluminum; and about 0.001 to about 0.005 weight percent boron. For example, Table 4 shows this example of the steel alloy, which contains these elements: iron, carbon, manganese, silicon, sulfur, chromium, nickel, molybdenum, aluminum, and boron.

TABLE 4

Example of a New Steel Alloy

C	Mn	Si	S	Cr	Ni	Mo	Al	B
(wt %)	(wt %)	(wt %)	(wt %)	(wt %)	(wt %)	(wt %)	(wt %)	(wt %)

0.25-0.50	1.50-2.00	0.30-0.60	0.05-0.12	0.20-0.60	0.50-0.90	0.15-0.40	0.02-0.04	0.001-0.005

The steel alloys shown in Table 3 or Table 4 may also contain vanadium in an amount not exceeding 0.20 weight percent, titanium in an amount not exceeding 0.20 weight percent, niobium in an amount not exceeding 0.20 weight percent, and nitrogen, wherein the nitrogen may be provided in the range of 0.01 to 0.04 weight percent.
In another example, a steel alloy may be provided that consists essentially of the following: about 0.35 weight percent carbon, about 1.65 weight percent manganese, about 0.45 weight percent silicon, about 0.4 weight percent chromium, about 0.7 weight percent nickel, about 0.25 weight percent molybdenum, and the balance iron. A small amount of boron, such as 0.001 to about 0.005 weight percent boron, could also be included. Preferably, sulfur should also be included, such as 0.05 to 0.12 weight percent sulfur. For example, Table 5 shows this example of the steel alloy, which contains these elements: iron, carbon, manganese, silicon, chromium, nickel, and molybdenum, and optionally boron and sulfur.

TABLE 5

Example of a New Steel Alloy

						B	S
C	Mn	Si	Cr	Ni	Mo	(wt %)	(wt %)
(wt %)	(wt %)	(wt %)	(wt %)	(wt %)	(wt %)	(opt.)	(opt.)

0.35	1.65	0.45	0.4	0.7	0.25	0.001-0.005	0.05-0.12

The new steel alloy may exhibit a time-temperature-transformation (TTT) featured diagram 100 as illustrated conceptually in FIG. 1. FIG. 1 is a conceptual illustration, and the new steel alloy need not have the exact phases corresponding to times and temperatures as shown in FIG. 1. Temperature is conceptually shown on the Y-axis, indicated at element 102, shown from a high of D7 degrees Celsius down to a low of 0 degrees Celsius; and time is shown on the X-axis at element 104.
At the highest temperatures, such as above D7, the steel alloy is already solidified and transformed into an austenite microstructure as indicated in section 106. As the steel alloy is cooled, it may undergo various phase transformations as a function of time. Before the time reaches time u1, corresponding to the nose 108 of the phase diagram 100, the steel alloy remains in an austenite form. Were the steel alloy to be cooled slowly through region 110, a ferrite and pearlite microstructure would be created. Were the steel alloy to be cooled a bit faster through region 112, a finer ferrite and pearlite microstructure would be created. In region 114, ferrite and coarse pearlite are formed. In region 116, ferrite and pearlite are formed. In region 118, fine pearlite is formed. A bainite formation temperature is indicated at 120. In region 122, 50% fine pearlite and 50% upper bainite are formed. In region 124, upper bainite is formed. In region 126, lower bainite is formed. On the left side of the diagram 100, metastable austenite is created in region 128, as when the steel alloy is quickly cooled to a temperature between D5 and D3, in an amount of time less than u1. Once the region 128 is entered, an isothermal process may be used to enter the bainite regions 124 and/or 126. Entering temperature D3 would cause martensite to begin to form in region 130, which would include martensite and slightly retained austenite until room temperature is reached.
To achieve a desired bainitic microstructure, the steel alloy may be cooled along the lines 136 and 138, wherein the surface of the cast steel alloy is cooled along the line 136, and the center of the cast steel alloy is cooled along the line 138. As such, the steel alloy is quickly cooled from temperature D7 to lower than D5 before time u1. Once the steel alloy is cooled to region 128, it is held at an approximately constant temperature D4 past the bainite start line 140 into region 112 and past the bainite finish line 142 into the bainite region 126 until bainitic transformation completes. At about time u2 or shortly thereafter in the region 128, the steel alloy begins to form a bainite microstructure. At line 142, bainite transformation completes.
FIG. 1 shows that the new steel alloy may be cooled quickly and directly from an austenite microstructure in austenite region 106 at a high temperature D7 down to a metastable austenite region 128, and then held at a constant temperature to achieve bainite in one of regions 124 and 126.
Referring now to FIG. 2, a temperature-time diagram of a steel alloy production process is illustrated. Temperature is illustrated on a Y-axis at 202 and time is illustrated on an X-axis at 204. Prior to time x0, the steel alloy is cast in a mold at a high temperature at or above T0. At time x0, solidification of the cast component is ceased, and the cast steel alloy component is allowed to cool in the mold until reaching temperature T1 at time x1. At temperature T1 corresponding to time x1, the case steel alloy component is shook out of the mold and air quenched (rapidly cooled) from temperature T1 to temperature T2, which corresponds to the time period between time x1 and time x2. The cast steel alloy component is then held at a constant temperature T2 until time x3. After time x3, the steel alloy can then be allowed to cool by air. The cooling process illustrated in FIG. 2 allows the cast steel alloy component to be cooled as shown along lines 136 and 138 in FIG. 1. Accordingly, the temperature T1 before shakeout represents a high temperature, such as D7 in FIG. 1, which is then rapidly cooled to temperature T2 along the lines 136 and 138 shown in FIG. 1. At temperate T2, the component is then held at a constant temperature T2, which corresponds to the temperature D4 in FIG. 1 until a large amount of bainite is achieved in region 126 at time x3.
Referring now to FIG. 3, the method of forming the cast steel alloy component having a bainitic microstructure as described in FIGS. 1 and 2 is illustrated as a process flow chart in FIG. 3. The process 300 includes a first step 302 of creating a liquid steel having one of the steel alloy compositions described above. In step 304, a mold is created. The mold may be a sand mold, such as a green sand mold, an investment mold, a shell mold, or another desired mold, by way of example.
The process or method 300 then includes a step 306 of pouring the hot liquid steel alloy into the mold and solidifying the cast steel alloy in the mold. The solidifying takes place above temperature T0 and before corresponding time x0, in FIG. 2.
Once the cast steel alloy is solidified and cooled to temperature T1, the method 300 includes a step 308 of shaking the cast steel alloy component out of the mold. With reference to FIG. 2, the shakeout occurs at temperature T1 and at corresponding time x1. In the method 300, T1 is in the range of 730-780 degrees Celsius. Thus, once the component in the mold reaches the range 730-780 (T1), shakeout occurs.
The method 300 then includes a step 310 of air quenching the cast steel alloy component down to the temperature T2. The temperature T2 is in the range of 420-530 degrees Celsius. After the temperature T2 is met through air quenching, the cast steel alloy component is held constant at the temperature T2 in a step 312 for a period of time between x2 and x3 as shown in FIG. 2. The period of time between x2 and x3 is between 1.5 hours and 3.5 hours. After the time period between x2 and x3 elapses, the method 300 may then include a step 314 of air cooling the cast component down to room temperature. If the component were to be air cooled prior to the time period in the step 312, the alloy would dip down into a martensite region 130, 132 under temperatures D2 or D1 (see FIG. 1) prior to forming the bainite. However, since the component is held at the temperature T2 for the desired period of time between x2 and x3 for “isothermal” processing, the phase lines 136, 138 may be followed to grow bainite before cooling the part further at time x3 in FIG. 2 into the bainite region 134, as shown in FIG. 1.
Thus, the step 312 of holding the component at an isothermal temperature T2 in the range of 420 to 530 Celsius may start immediately after the step 310 of air quenching and continue for a time period in the range of 1.5 to 3.5 hours. In some variations, the step 312 is performed immediately after the step 314 without cooling the component to a temperature below 420 degrees Celsius between the step 310 of air quenching and the step 312 of holding the component at the isothermal temperature T2. In this way, the heat that already exists in the part as it is cooling after solidification can be used without wasting the heat and having to reheat the part to create bainite.
Thus, the new steel alloy is already strong and hard, with a bainite microstructure, without the need for additional reheating, quenching, austempering, and tempering. Accordingly, time and cost are saved from not having to perform reheating, quenching, austempering, and tempering.
The fine grain steel alloys described herein may be used to manufacture a steel automotive component. Therefore, it is within the contemplation of the inventors herein that the disclosure extend to steel automotive components, including but not limited to crankshafts, transmission shafts, transmission cases, half shafts, axle shafts, and the like. For example, referring to FIGS. 4A-4B, a crankshaft 400 is illustrated, which is made of any variation of the steel alloy described herein. The crankshaft 400 may have hollow journals 402 created by the casting procedure 300 (or by another casting procedure or method).
Furthermore, while the above examples are described individually, it will be understood by one of skill in the art having the benefit of this disclosure that amounts of elements described herein may be mixed and matched from the various examples within the scope of the appended claims.
It is further understood that any of the above described concepts can be used alone or in combination with any or all of the other above described concepts. Although an embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this disclosure. For that reason, the following claims should be studied to determine the true scope and content of this invention.

Claims

What is claimed is:

1. A high-strength steel alloy comprising:

iron;

about 0.24 to about 0.80 weight percent carbon;

about 0.40 to about 2.10 weight percent manganese;

about 0.20 to about 1.60 weight percent silicon;

about 0.05 to about 0.14 weight percent sulfur;

about 0.10 to about 12.0 weight percent chromium;

about 0.10 to about 2.50 weight percent nickel; and

about 0.02 to about 0.07 weight percent aluminum.

2. The high-strength steel alloy of claim 1, further comprising boron in an amount not exceeding 0.005 weight percent.

3. The high-strength steel alloy of claim 2, wherein the iron is provided in an amount between about 75.0 and about 98.88 weight percent.

4. The high-strength steel alloy of claim 3, further comprising molybdenum in an amount not exceeding 0.60 weight percent.

5. The high-strength steel alloy of claim 4, further comprising vanadium in an amount not exceeding 0.20 weight percent.

6. The high-strength steel alloy of claim 5, further comprising titanium in an amount not exceeding 0.20 weight percent.

7. The high-strength steel alloy of claim 6, further comprising niobium in an amount not exceeding 0.20 weight percent.

8. The high-strength steel alloy of claim 7, further comprising about 0.01 to about 0.04 weight percent nitrogen.

9. The high-strength steel alloy of claim 2, wherein the high-strength steel alloy comprises:

about 0.24 to about 0.40 weight percent carbon;

about 1.50 to about 2.00 weight percent manganese;

about 0.40 to about 0.80 weight percent silicon;

about 0.05 to about 0.12 weight percent sulfur;

about 0.10 to about 0.60 weight percent chromium;

about 0.60 to about 0.90 weight percent nickel;

about 0.20 to about 0.40 weight percent molybdenum;

about 0.02 to about 0.04 weight percent aluminum; and

about 0.001 to about 0.005 weight percent boron.

10. The high-strength steel alloy of claim 2, wherein the high-strength steel alloy comprises:

about 0.25 to about 0.50 weight percent carbon;

about 1.50 to about 2.00 weight percent manganese;

about 0.30 to about 0.60 weight percent silicon;

about 0.05 to about 0.12 weight percent sulfur;

about 0.20 to about 0.60 weight percent chromium;

about 0.50 to about 0.90 weight percent nickel;

about 0.15 to about 0.40 weight percent molybdenum;

about 0.02 to about 0.04 weight percent aluminum; and

about 0.001 to about 0.005 weight percent boron.

11. A crankshaft for an automotive propulsion system, created from a high-strength steel alloy according to claim 10.

12. A crankshaft for an automotive propulsion system, created from a high-strength steel alloy according to claim 1.

13. The high-strength steel alloy of claim 2, having an ultimate tensile strength in the range of 750 to 1100 MPa.

14. The high-strength steel alloy of claim 13, having an ASTM grain size number in the range of 5 to 8.

15. A high-strength steel alloy consisting essentially of:

about 0.35 weight percent carbon;

about 1.65 weight percent manganese;

about 0.45 weight percent silicon;

about 0.4 weight percent chromium;

about 0.7 weight percent nickel;

about 0.25 weight percent molybdenum; and

the balance iron.

16. A method of forming a steel alloy component, the method comprising:

creating a steel alloy comprising iron, about 0.24 to about 0.80 weight percent carbon, about 0.40 to about 2.10 weight percent manganese, about 0.20 to about 1.60 weight percent silicon, about 0.05 to about 0.14 weight percent sulfur, about 0.10 to about 12.0 weight percent chromium, about 0.10 to about 2.50 weight percent nickel, and about 0.02 to about 0.07 weight percent aluminum;

casting in a mold the steel alloy to form the component;

shaking out the mold; and

air quenching the component until the component has a temperature in the range of 420 to 530 degrees Celsius.

17. The method of claim 16, further comprising:

holding the component at an isothermal temperature in the range of 420 to 530 Celsius starting immediately after the step of air quenching and continuing for a time period in the range of 1.5 to 3.5 hours.

18. The method of claim 17, wherein the step of holding the component at the isothermal temperature is performed immediately after the step of air quenching without cooling the component to a temperature below 420 degrees Celsius between the step of air quenching and the step of holding the component at the isothermal temperature.

19. The method of claim 18, wherein the step of creating the steel alloy further comprises creating the steel alloy comprising boron in an amount not exceeding 0.005 weight percent.