CN103341695A - Method for improving mechanical property of hardened and tempered low-alloy high-strength steel GMAW connector - Google Patents

Abstract

The invention discloses a method for improving the mechanical property of a hardened and tempered low-alloy high-strength steel GMAW connector so as to solve the problems that when hardened and tempered low-alloy high-strength steel through quenching plus low temperature tempering is welded, tempering softening happens to one of heat affected zones of a welded joint, so that the quality of the welded joint is reduced. The method is characterized in that the texture of a softened area of the welded joint is improved with the help of the thermal cycle characteristic that the heating rate and cooling rate of laser are high ; laser remelting is conducted on the softened area of the welded joint to reduce the width of the softened area with the help of the characteristics that a welded line is deep, the aspect ratio is high, thermal input is low, a heat affected zone is small, and welding deformation is slight in laser welding deep penetration welding; therefore, the strength and toughness of the hardened and tempered low-alloy high-strength steel GMAW connector through quenching plus low temperature tempering can be improved.

Description

A kind of method of improving modified low-alloy high-strength steel GMAW joint mechanical property

[technical field]

The invention belongs to the materials processing technology field, relate to a kind of method of improving modified low-alloy high-strength steel GMAW joint mechanical property.

[background technology]

Low-alloy high-strength steel with the intensity of its superelevation, good plasticity and toughness and preferably welding performance be widely used in fields such as engineering machinery, electric power, pressure vessel, automobile.The kind of low-alloy high-strength steel can be divided into non-hardened and tempered steel and quenched and tempered steel, the low-alloy high-strength steel of quenched and tempered state is to develop the rapidest, one of the most great-hearted steel grade in recent decades, its yield strength can reach 880～1176MPa, because the intensity of its superelevation, good plasticity and toughness and weldability, except being widely used in fields such as bridge, building, boats and ships, high-pressure bottle, engineering machinery and vehicles, usually also be used for very high product or the parts of requirement of strength, as rocket engine shell, undercarriage etc.

Because excellent performance and remarkable in economical benefits, the application of modified low-alloy high-strength steel in the engineering Welding Structure is increasingly extensive, and to how the welding structural element of obtained performance excellence is researcher's primary study target always.For modified low-alloy high-strength steel, common problem except the high-strength steel welding, welding cold cracking and welding heat affected zone embrittlement, the softening problem of welding point also is the key technical problem that this steel grade runs in welding, this is because modified low-alloy high-strength steel is to add the alloying element that improves quenching degree on the basis of mild steel to obtain the intensity height by modified (quenching+tempering) heat treatment, the low-carbon martensite of good toughness+lower bainite line and staff control, and when welding, under the Thermal Cycle effect, the joint heat affected area is heated to the zone that surpasses modified temperature, intensity will appear, hardness is lower than the softened zone of mother metal, this softened zone may become the weak area of strength of joint, the softening problem of welding point namely occurs.Postwelding if martensite is able to self tempering in annealing process, can be alleviated the situation that cold crack occurs; If but cooling velocity is fast, martensite can not self tempering, and its cold cracking inclination must strengthen.Studies show that low-alloy high-strength steel welds under quality adjustment condition, crackle and embrittlement can be controlled by measures such as preheating and postweld heat preservations, and the softening problem that causes can't solve at postwelding, need be controlled in welding procedure.For example, people such as Wang Lianfang weld research to the DILLMAX965 quenching and tempering, high that France excellent Jino iron company produces, and studies show that, have only by the input of strictness control heat to make t _8/5During＜10s, just there is not ruckbildung in the heat affected area in the welding point.People such as Zhao Yuzhen weld research to the SS400 steel, studied the fine structure of its pulse MAG (80%Ar+20%CO2) welding point coarse grain zone, it studies show that when adopting high heat input to weld, the coarse grain zone, heat affected area contains a large amount of upper bainite tissues, and adopt when hanging down the heat input welding, the heat affected area is mainly the good lower bainite tissue of toughness, ruckbildung do not occur in the heat affected area.Sum up above method, as can be known, reduce as far as possible and avoid the softening effective means in heat affected area when the heat input is the welding of quenched and tempered state high-strength steel, but this method has brought the disappearance of limitation and flexibility also for the high-strength steel welding manner, therefore, find other methods that effectively solve the softening problem in modified low-alloy high-strength steel GMAW joint heat affected area to have very necessary.

[summary of the invention]

When welding at modified low-alloy high-strength steel GMAW, temper softening takes place in welding point HAZ (heat affected area), makes the problem that strength of joint descends to the invention provides a kind of method of improving modified low-alloy high-strength steel GMAW joint mechanical property.

The present invention is achieved through the following technical solutions:

A kind of method of improving modified low-alloy high-strength steel GMAW joint mechanical property comprises following operation:

1) measures and demarcate the weld seam of welding point, the position of melt run, calculate position and the width that formula calculated and demarcated the welding point softened zone according to the maximum temperature of welding thermal cycle curve;

2) adopt laser that the softened zone of welding point is carried out remelting;

3) joint surface behind the laser remolten is carried out grinding process.

Described softened zone refers to take place in the welding point heat affected area zone that tensile strength is lower than mother metal tensile strength.

Described when the softened zone is carried out remelting, can adopt the mode of single face or two-sided laser remolten to reach the remelting of butt joint softened zone.

Describedly before measure demarcating the welding point softened zone, also comprise following processing:

The sample joint surface that at first will treat laser remolten carries out sanding and polishing;

Adopt corrosive agent to corrode to welding point then, until each zone that shows joint welding, melt run, heat affected area and mother metal.

Described corrosive agent refers to can be used for the corrosive agent of metal metallographic corrosion analysis.

Described GMAW joint welds formed welding point for the modified low-alloy high-strength steel thin plate of quenching+lonneal GMAW.

Described thin plate refers to that thickness range is the steel plate of 0.2～6mm.

The remelting of described butt joint softened zone refers to butt joint softened zone penetration or the capable remelting of non-penetration.

Being calculated as of the position of described welding point softened zone and width:

Maximum temperature according to the weld cycle curve is calculated formula:

$\frac{1}{T_{\max }-T_0}=\frac{4.13c_v\mathrm{\δd}}{E}+\frac{1}{T_M-T_0}---\left(1\right)$

In the formula: E is the sweating heat input; T ₀Be the weldment initial temperature; T _MBe the mother metal fusing point, d is the distance of leaving melt run; δ is mother metal thickness; c _vBe the material specific heat at constant volume;

Derive peak temperature T among the joint HAZ _MaxThe melt run distance is left in the position

$d=(\frac{1}{T_{\max }-T_0}-\frac{1}{T_M-T_0})\frac{E}{4.13c_v\mathrm{\δ}}---\left(2\right)$

Then the width of softened zone is among the joint HAZ:

$b=d_{T_{\max }=T_h}-d_{T_{\max }=A_{c1}}=(\frac{1}{T_h-T_0}-\frac{1}{A_{c1}-T_0})\frac{E}{4.13c_v\mathrm{\δ}}---\left(3\right)$

B is HAZ softened zone width in the formula; T _hBe the cold production self tempering temperature of material control;

Be position and the melt run distance of temperature for peak temperature among the HAZ; Be peak temperature A among the HAZ _C1Position and melt run distance.

Compared with prior art, the present invention has following beneficial technical effects:

The method of the modified low-alloy high-strength steel GMAW of improvement provided by the invention joint mechanical property, be a kind of method based on the modified low-alloy high-strength steel thin plate of laser remolten method improvement quenching+lonneal GMAW joint softened zone mechanical property, improve the tissue of the GMAW joint HAZ softened zone of the modified low-alloy high-strength steel thin plate of quenching+lonneal by the fast thermal cycle characteristics of LASER HEATING cooling velocity; Than the characteristics high, that the little heat affected area of heat input is little, welding deformation is little the GMAW joint of the modified low-alloy high-strength steel thin plate of quenching+lonneal is carried out laser remolten and can reduce joint HAZ softened zone width by laser weld deep penetration welding weld seam is dark, wide, can improve the joint obdurability with this.

[description of drawings]

Fig. 1 demarcates and the softened zone position view for joint area;

Fig. 2 is joint laser remolten scheme schematic diagram;

Fig. 3 is macro morphology schematic diagram behind the joint laser remolten;

Joint pictorial diagram behind Fig. 4 embodiment laser remolten;

Fig. 5 is joint tensile sample stress-strain curves before and after the laser remolten.

[specific embodiment]

The present invention is described in further detail below in conjunction with specific embodiment.

A kind of method of improving modified low-alloy high-strength steel GMAW joint mechanical property provided by the invention comprises following operation:

1) measures and demarcate the weld seam of welding point, the position of melt run, calculate position and the width that formula calculated and demarcated the welding point softened zone according to the maximum temperature of welding thermal cycle curve;

2) adopt laser that the softened zone of welding point is carried out remelting;

3) joint surface behind the laser remolten is carried out grinding process.

Concrete, before measuring demarcation welding point softened zone, also comprise following processing:

The sample joint surface that at first will treat laser remolten carries out sanding and polishing;

Adopt corrosive agent to corrode to welding point then, until each zone that shows joint welding, melt run, heat affected area and mother metal.Described corrosive agent refers to can be used for the corrosive agent of metal metallographic corrosion analysis.

Described softened zone refers to take place in the welding point heat affected area zone that tensile strength is lower than mother metal tensile strength.And when the softened zone is carried out remelting, can adopt the mode of single face or two-sided laser remolten to reach the remelting of butt joint softened zone.The remelting of described butt joint softened zone refers to butt joint softened zone penetration or the capable remelting of non-penetration.

Providing specific embodiment below describes.

Present embodiment adopts JHM-1GXY-400X type Nd:YAG laser instrument that the thick 1000MPa fine grain, high strength of 1.5mm steel 20MnTiB GMAW joint HAZ softened zone is carried out laser remolten.Concrete implementation step comprises:

(1) adopt GMAW welding 20MnTiB banjo fixing butt jointing, protective gas is rich argon mixture gas, and heat input is 9.5J/cm.Adopting line to cut treats specifically to be of a size of 200mm * 30mm * 1.5mm by the laser remolten sample.

(2) the sample joint for the treatment of laser remolten carries out sanding and polishing.

(3) the good sample of sanding and polishing is corroded 20MnTiB GMAW welding point zone with 4% nital (volume fraction), until each zone that shows joint welding, melt run, heat affected area and mother metal,

(4) in conjunction with metallographic observation and, measure to demarcate weld seam, melt run, the heat affected area of 20MnTiB GMAW joint, calculate position and the width that formula calculated and demarcated the welding point softened zone according to the maximum temperature of welding thermal cycle curve, concrete steps are as follows:

Maximum temperature by welding thermal cycle curve is calculated formula:

$\frac{1}{T_{\max }-T_0}=\frac{4.13c_v\mathrm{\δd}}{E}+\frac{1}{T_M-T_0}---\left(1\right)$

Derive peak temperature T among the joint HAZ _MaxThe melt run distance is left in the position

$d=(\frac{1}{T_{\max }-T_0}-\frac{1}{T_M-T_0})\frac{E}{4.13c_v\mathrm{\δ}}---\left(2\right)$

Then the softened zone width is among the joint HAZ

$b=d_{T_{\max }=T_h}-d_{T_{\max }=A_{c1}}=(\frac{1}{T_h-T_0}-\frac{1}{A_{c1}-T_0})\frac{E}{4.13c_v\mathrm{\δ}}---\left(3\right)$

Among the embodiment: heat input E is 8.2kJ/cm; Weldment initial temperature T ₀It is 20 ℃; 20MnTiB fusing point T _MIt is 1530 ℃; Mother metal thickness δ is 6mm; The specific heat at constant volume c of 20MnTiB _vBe 6.7J/ (cm ³℃); 20MnTiB is controlled cold production temperature T _hIt is 200 ℃; Then by formula (2) as can be known, peak temperature is that the position of temperature and melt run are apart from d among the joint HAZ _Tmax=T _hBe 4mm; Peak temperature A among the joint HAZ _C1Position and melt run are apart from d _Tmax=A _ClBe 2.5mm.Schematic diagram is Fig. 1.

(5) adopt JHM-1GXY-400X type Nd:YAG laser instrument that the 20MnTiBGMAW joint HAZ softened zone of demarcating is carried out remelting;

Concrete scheme is: 1. adopt pulse laser to the GMAW joint softened zone remelting of 20MnTiB, schematic diagram is Fig. 2;

2. for reducing the heat input, avoid producing the wideer LASER HEAT zone of influence and produce little welding deformation, the GMAW joint of 20MnTiB is carried out the mode of the little heat input of twice butt welding up and down, reach the remelting of butt joint HAZ softened zone, schematic diagram is Fig. 3, and Fig. 4 is the embodiment pictorial diagram;

(6) joint behind the laser remolten is carried out grinding process.

The example sample is carried out mechanical property to be detected, the detection method of taking is the test of joint tensile property, Fig. 5 is the resulting stress-strain curves of embodiment joint straight draw test, black curve is without crossing laser remolten softened zone joint stress-strain curve of tensile among the figure, curve shows that the tensile strength of joint is 766MPa, curve red among the figure is the joint stress-strain curve of tensile through the laser remolten softened zone, curve shows that the tensile strength of joint is 906MPa, from the contrast of two curves as can be seen laser remolten can improve the mechanical property of the GMAW joint softened zone of 20MnTiB significantly.

Explanation is at last, present embodiment is only unrestricted in order to technical scheme of the present invention to be described, other modifications that the ability those of ordinary skill is made technical scheme of the present invention or be equal to replacement, only otherwise break away from the spiritual scope of technical solution of the present invention, all should be encompassed in the claim scope of the present invention.

Claims (9)

1. a method of improving modified low-alloy high-strength steel GMAW joint mechanical property is characterized in that, comprises following operation:

1) measures and demarcate the weld seam of welding point, the position of melt run, calculate position and the width that formula calculated and demarcated the welding point softened zone according to the maximum temperature of welding thermal cycle curve;

2) adopt laser that the softened zone of welding point is carried out remelting;

3) joint surface behind the laser remolten is carried out grinding process.

2. the method for the modified low-alloy high-strength steel GMAW of improvement as claimed in claim 1 joint mechanical property is characterized in that, described softened zone refers to take place in the welding point heat affected area zone that tensile strength is lower than mother metal tensile strength.

3. the method for the modified low-alloy high-strength steel GMAW of improvement as claimed in claim 1 joint mechanical property is characterized in that, when the softened zone was carried out remelting, the mode of employing single face or two-sided laser remolten reached the remelting of butt joint softened zone.

4. the method for the modified low-alloy high-strength steel GMAW of improvement as claimed in claim 1 joint mechanical property is characterized in that, also comprises following processing before measuring demarcation welding point softened zone:

The sample joint surface that at first will treat laser remolten carries out sanding and polishing;

Adopt corrosive agent to corrode to welding point then, until each zone that shows joint welding, melt run, heat affected area and mother metal.

5. the method for the modified low-alloy high-strength steel GMAW of improvement as claimed in claim 4 joint mechanical property is characterized in that, described corrosive agent refers to can be used for the corrosive agent of metal metallographic corrosion analysis.

6. the method for the modified low-alloy high-strength steel GMAW of improvement as claimed in claim 1 joint mechanical property is characterized in that, described GMAW joint welds formed welding point for the modified low-alloy high-strength steel thin plate of quenching+lonneal GMAW.

7. the method for the modified low-alloy high-strength steel GMAW of improvement as claimed in claim 6 joint mechanical property is characterized in that, described thin plate refers to that thickness range is the steel plate of 0.2～6mm.

8. the method for the modified low-alloy high-strength steel GMAW of improvement as claimed in claim 1 joint mechanical property is characterized in that, the remelting of described butt joint softened zone refers to butt joint softened zone penetration or the capable remelting of non-penetration.

9. the method for the modified low-alloy high-strength steel GMAW of improvement as claimed in claim 1 joint mechanical property is characterized in that, being calculated as of the position of welding point softened zone and width:

Maximum temperature according to the weld cycle curve is calculated formula:

$\frac{1}{T_{\max }-T_0}=\frac{4.13c_v\mathrm{\δd}}{E}+\frac{1}{T_M-T_0}---\left(1\right)$

In the formula: E is the sweating heat input; T ₀Be the weldment initial temperature; T _MBe the mother metal fusing point, d is the distance of leaving melt run; δ is mother metal thickness; c _vBe the material specific heat at constant volume;

Derive peak temperature T among the joint HAZ _MaxThe melt run distance is left in the position

$d=(\frac{1}{T_{\max }-T_0}-\frac{1}{T_M-T_0})\frac{E}{4.13c_v\mathrm{\δ}}---\left(2\right)$

Then the width of softened zone is among the joint HAZ:

$b=d_{T_{\max }=T_h}-d_{T_{\max }=A_{c1}}=(\frac{1}{T_h-T_0}-\frac{1}{A_{c1}-T_0})\frac{E}{4.13c_v\mathrm{\δ}}---\left(3\right)$

B is HAZ softened zone width in the formula; T _hBe the cold production self tempering temperature of material control; d _Tmax=T _hBe position and the melt run distance of temperature for peak temperature among the HAZ; d _Tmax=A _ClBe peak temperature A among the HAZ _C1Position and melt run distance.

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