JPS5853713B2 - Steel for brake discs with excellent cracking resistance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a steel for brake discs which is improved and has excellent cracking resistance so that brittle fracture does not occur in brake discs.

In general, the performances required for hat-shaped brake discs used in railway vehicles, etc. are (1) strength, (2) toughness, (3) heat cracking resistance, (4) wear resistance, and (5) heat deformation resistance. can be given.

In this S, (5) is a performance that depends on the shape, and it is necessary to consider the performances (1) to (4) for the material.

By the way, it is thought that the breakage that occurs on the brake disc occurs through the following process.

That is, (1) Thermal cracks occur due to the brakes ([[)
It consists of three stages: (1) the thermal crack grows due to repeated braking, and (e) the thermal crack grows to a critical length and breaks brittle.

The strength of a hat-shaped brake disc is determined by the brake structure, and it is sufficient to satisfy the design strength, and there is no problem with wear resistance.

Therefore, improving the toughness and heat cracking resistance will enhance the performance as a brake.

Preventing brittle fracture requires a high toughness material that still does not reach the fracture toughness value even if a crack penetrates through the disk plate.

By the way, as the toughness of steel materials increases, the strength generally decreases, so it is important to select the optimal combination of strength and toughness based on chemical composition and heat treatment.

Due to the design of the brake disc, the tensile strength is 60K.
g f /mA or more is required.

Further, the fracture toughness value Kc is determined by applying fracture mechanics to a value that does not cause breakage even if a thermal crack penetrates through the thickness of the disk.

For example, if the crack depth is 40mm, then σ: tensile residual stress accumulated in the disc due to repeated braking ※※a: crack depth where a-40kgf/mt? t.

If a-407n71L is used, it is not possible to completely eliminate the occurrence of thermal cracks using current technology, but it is known that the improvement can be achieved by reducing the amount of carbon, and 0.40% or less is desirable.

Furthermore, since wear resistance depends on hardness, it is desirable that the hardness is higher than that of currently used materials, that is, HB>220.

The present invention proposes a steel for brake discs that satisfies the properties necessary to prevent brittle fracture as described above and has excellent cracking resistance.

That is, the present invention provides C0.30 to 0.40%, si
o, 15-0.60%, Mn 0.50-1.40%,
Ni 1.50-3.00%, CrO, 60% or more1.
less than 20%, Mo 0.15-0.80%, and so
l, AIo, 015-0.060% and Vo, 05-0.
The object of the present invention is to provide a steel for brake discs containing 30% of one or two kinds of Fe, with the remainder being substantially Fe, and having excellent cracking resistance.

The reason for limiting the chemical components in this invention is as follows.

C is necessary to impart strength and wear resistance, but 0.
If it is less than 30%, a sufficient effect will not be achieved, and if it exceeds 0.40%, sufficient fracture toughness will not be obtained and there is a risk of cracking during quenching, so the content is set at 0.30 to 0.40%.

Si is a necessary element for deoxidizing molten steel, but if it is less than 0.15%, its effect is insufficient, and if it exceeds 0.60%, sufficient fracture toughness cannot be obtained and nonmetallic inclusions also increase. Therefore, it is set to 0.15 to 0.60%.

Mn is a woody element that is effective in deoxidizing, desulfurizing, and improving the strength of molten steel, but if it is less than 0.50%, the effect is insufficient, and if it exceeds 1.4%, nonmetallic inclusions will increase. from,
The content should be 0.50 to 1.4%.

Ni content of 1.5% or more improves toughness, but the upper limit is set to 3.0% due to effects on mechanical properties, fracture toughness, heat cracking resistance, and economical reasons.

Cr needs to be contained at 0.6% or more to improve hardenability, but 1.2% is required for ill for the same reason as nickel.
less than

Mo is effective in suppressing tempering brittleness and improving toughness, but if it is less than 0.15%, it has no effect, but excessive addition is undesirable, and for the same reason as Ni, the upper limit is set to 0. .80%.

sol, AI, and V are effective in improving the fracture toughness value due to the effect of refining crystal grains, and it is sufficient to contain either one of them, but they may also be contained in combination.

Sol, Al is less than 0.015%, ■ is 0.05%
If it is less than 0.0, there is no effect, and sol and AI are 0.0.
When it exceeds 60%, nonmetallic inclusions increase, and ■ is 0.30.
% is undesirable because the fracture toughness value decreases due to secondary hardening.

Further, although P1S is not particularly limited, all of them are harmful impurities, and it is desirable to reduce them as much as possible.

Next, embodiments of the invention will be described.

Inventive steels A to E according to the present invention and conventional steel for comparison, the chemical components of which are shown in Table 1, were melted and subjected to conventional hot rolling to obtain hot rolled steel sheets for brake discs.

Test pieces were taken from each of the above steels, and subjected to tensile tests, hardness tests,
And an impact test was conducted.

The results are shown in Table 2**, Table 3, and Table 4.

The test was carried out using Comp with the same thickness as the actual brake disc.
Act Ten5io rock test piece (as specified by ASTM) was used.

Therefore, although it is not KIC defined by linear fracture mechanics, it is sufficient as a criterion for determining actual breakage loss.

Note that the above values are as shown in Table 5 when converted into allowable crack lengths.

In addition, an actual brake test was conducted using a dynamometer brake tester that can reproduce actual driving conditions.

In other words, the most severe initial velocity dust is 210kllil/
The stop brake was applied repeatedly from h.

As a result, the product using conventional steel suffered a breakage loss after 134 cycles, but the product using this invention steel A did not cause any breakage loss even after 350 cycles. It can be seen that brake discs using this material have excellent breakage resistance.

Claims (1)

[Claims] I C0.30~0.40%, Si0.15~0.6
0%, Mn 0.50~1.40%, Ni 1.50~
3.00%, CrO, 60% or more but less than 1.2%, Mo
0.15-0.80%, further sol, AI 0.0
A steel for brake discs having excellent cracking resistance, containing one or both of 15 to 0.060% of VO and 05 to 0.30% of VO, with the remainder being substantially Fe.