CN101270459B - Method for improving welded joint fatigue strength following chilling treatment after weld toe TIG refusion - Google Patents

Abstract

The invention discloses an after-welding processing method by using a welding joint after being remelted by a welding toe TIG to follow a spray chilling treatment to adjust the residual stress field of the weld toe to transfer the original residual tension stress field of the TIG remelting area into a compression stress field which is beneficial to improve the endurance strength of the joint. Themethod integrates both the advantages of improving the geometrical shape of the welding toe by TIG remelting and improving the residual stress state of the welding toe by the chilling treatment in theremelting area; besides, the method has the advantages of simple device, convenient operation, remarkable effect, easily checked and controlled quality, no noise, no environment pollution, etc. The method can be applied to the non-quenching steels like mild steel low alloyed steel, etc., as well as the welding structures of the metals like aluminum alloy and titanium alloy. The method can be popularized and applied in the industrial fields of shipping and ocean platforms, rolling stocks, railroad bridges, cranes, oil pipelines and chemical containers.

Description

The method of toe of weld TIG remelting heel improving welded joint fatigue strength following chilling treatment

Technical field

The invention belongs to welding technique and engineering field, the welded construction that relates generally to soft steel, low alloy steel is improved a kind of after welding treatment method of welded joint fatigue strength by adjusting toe of weld surface residual stress field.

Background technology

Toe of weld TIG remelting (molten repairing) technology is a kind of after welding treatment method of improving welded joint fatigue strength that International Institude of Welding (IIW) is recommended, this method is to be thermal source with the tungsten argon arc, with the toe of weld refuse, defectives such as the undercut that removing may exist, micro-slag inclusion, form the uniform reflow zone of transition simultaneously, make between weld seam and the mother metal and realize rounding off, reduce stress concentration, improve the fatigue strength of joint.Compare with other processing method that improves welded joint fatigue strength, it is simple that TIG remelting technology has technology, easy to use, cheap, do not have an advantage such as noise, therefore be applied at industrial circles such as shipbuilding and ocean platform, rail truck, railroad bridge, lifting machine, oil pipeline, pressures vessels for the chemical industry.

But, after utilizing TIG electric arc that toe of weld is reheated fusing, cooled and solidified, the toe zone still presents high residual-tensile stress state, make that the effect of improving joint fatigue strength is restricted greatly, the degree that the fatigue strength of butt junction simultaneously improves also exists marked difference, the fatigue data discreteness is big, sometimes even exist to reduce the possibility of joint fatigue strength.Therefore eliminating the toe of weld residual tension is the key that addresses the above problem.The method that tradition is eliminated unrelieved stress mainly contains oscillating aging processing (VRS) and the processing of integral solder structure stress relief annealing.The former needs specific equipment, and the effect of removal unrelieved stress is very limited; It is better that the latter eliminates the effect of unrelieved stress, and power consumption is big, efficient is low but integrally annealed is handled.For large welded structures, as bridge, hull, ocean platform etc., adopting these two kinds of methods to carry out bulk treatment objectively also is being impossible realize.

Summary of the invention

The objective of the invention is: handle with the spray Quench by Q345 steel toe of weld TIG remelting heel and adjust the residual stress field, toe zone, make the residual tension on toe of weld surface change two-way compressive stress state into, thereby improve the fatigue strength of welding joint greatly, improve the reliability and the work-ing life of welded construction safe operation.

Technical scheme of the present invention is: in the toe zone of welding joint (butt joint or corner connection), with TIG electric arc toe of weld is carried out heat fused, when reflow zone under air naturally cooling, solidify and when dropping to certain temperature, water sprays processing as heat-eliminating medium to remelted layer, this district's metal is promptly shunk form two-way stress field.

The concrete steps of the method for Q345 steel toe of weld TIG remelting heel improving welded joint fatigue strength following chilling treatment are:

(1) before the processing, removes lip-deep iron rust of toe of weld and splash earlier, clear up with grinder buffing;

(2) be that thermal source carries out remelting according to pre-set processing parameter along toe of weld with TIG electric arc, the angle between arc axis and the plummet is 0 °～30 °, and is positioned at 0.5mm～1.5mm place, the toe of weld outside;

(3) when toe of weld TIG reflow zone temperature was reduced to more than the critical temperature 100 ℃～200 ℃, water sprayed processing as low-temperature receiver to reflow zone, the temperature adjustment of TIG reflow zone when low-temperature receiver intensity is handled according to material, thickness of slab and Quench;

(4) after toe of weld TIG reflow zone Quench is handled, weldment is dried in case get rusty;

Q345 steel toe of weld TIG remelting processing parameter is: the tungsten electrode diameter: φ 3.2mm, and nozzle diameter: φ 12mm, shielding gas are argon gas; argon flow amount is 10～12L/min, and electric current is 170～180A, and voltage is 14～18V; speed is 13～16cm/min, and critical temperature is 450 ℃.

Q345 steel toe of weld TIG remelting heel is handled the principle of regulating the residual stress field with Quench: under as-welded, weld seam and nearly seam district (comprising toe of weld) thereof are the residual tension state.Handle in the welding toe remelting with TIG electric arc, be equivalent to not add the TIG welding process of filler metal.In the heat-processed of TIG electric arc, toe of weld reflow zone heat fused forms liquid metal bath, than the effect of contraction of cool region metal, has formed uneven compressive plastic deformation around the solid metal expanded by heating of its adjacent domain, thermal expansion amount are subjected to; In process of cooling, the reflow zone liquid metal solidification is subjected to the constraint of solid metal on every side and forms residual tension when shrinking, contiguous reflow zone and this part solid metal that compressive plastic deformation taken place also are subjected to metal around it in varying degrees stretching action, finally form residual tension.As seen, toe of weld is by still being two-way residual tension field after the TIG remelting.

When after toe of weld TIG reflow zone is solidified, being reduced to a certain temperature, using water as the Quench source toe of weld reflow zone surface is sprayed processing, the reflow zone and the contiguous position that are tensile stress state are shunk rapidly.When string stress overcame the yield strength of material under this temperature, reflow zone produced the stretching plastic deformation.If the reflow zone temperature surpasses a certain threshold value, then its stretching plastic deformation has also remained stretching plastic deformation's amount when all offsetting original compressive plastic deformation amount.When toe of weld reflow zone cool to room temperature, this remaining stretching plastic deformation is subjected to the rigidity squeezing action of metal on every side and forms two-way residual compressive stress field.

If it is Tcr that toe of weld TIG reflow zone is carried out the critical temperature of Quench processing, then

When T＜Tcr, reflow zone is the residual tension state

When T＞Tcr, reflow zone is the residual compressive stress state

When T=Tcr, reflow zone is stressless criticality

For the Q345 structural low welding assembly of thickness 14mm, the critical temperature value Tcr that toe of weld TIG reflow zone is carried out the Quench processing is 450 ℃.

Advantage of the present invention is: 1) handle by the Quench to toe of weld TIG electric arc reflow zone, can form the residual compressive stress field on the toe of weld top layer, improved the fatigue strength of welding joint significantly; 2) this processing method has been taken into account the TIG remelting and is improved toe of weld geometrical shape and reflow zone Quench and handle and improve toe of weld residual stress state advantage separately, and it is simple, easy to operate to have equipment, effect is remarkable, quality is checked and control easily, there is not noise, advantage such as free from environmental pollution is easy to promote the use of; 3) can replace toe of weld grinder buffing technology and postwelding one-piece construction annealing method, increase substantially production efficiency, reduce energy consumption and manufacturing cost; 4) applied widely.Not only can be used for non-hardened steel such as ordinary low-carbon steel, structural low, also can promote the use of in metallic substance such as aluminium alloy, titanium alloys.Can be applicable in industries such as boats and ships, machinery, vehicle, metallurgy, oil, chemical industry.

Description of drawings

The invention will be further described below in conjunction with the drawings and specific embodiments.

Fig. 1 is that toe of weld TIG remelting heel is with Quench treatment process process synoptic diagram

Embodiment

Embodiment 1

Quench treatment process after the toe of weld TIG remelting of configuration in railroad truck welded frame T shape corner joint.Material selection Q345-C structural low (thickness 14mm), toe of weld TIG remelting processing parameter: tungsten electrode diameter phi 3.2mm, nozzle diameter φ 12mm, argon flow amount 10L/min, electric current 170～180A, voltage 14～18V, speed 13～16cm/min.During the TIG remelting, the angle of welding torch and riser is about 30 °, and arc axis is positioned at 1～1.5mm place, the toe of weld outside.Toe of weld TIG remelted layer Quench treatment process: toe of weld TIG remelted layer temperature drops to when being not less than 500 ℃, the current that will have certain pressure spray toe of weld reflow zone surface by special nozzle and carry out the Quench processing, leave suitable distance between water jet and the tig torch, be not less than 500 ℃ to guarantee spray position remelted layer temperature.Adopt the result of blind hole method test welding toe unrelieved stress: under as-welded, the σ x=167MPa of parallel bead direction, the σ y=126MPa of vertical weld direction; After the toe of weld TIG remelting, σ x=161MPa, σ y=67MPa; Spray is handled during toe of weld TIG remelting postcooling to 550 ℃, σ x=-176MPa, σ y=-123MPa.Obviously, handle the back by this processing method and form two-way stress field in the toe zone.Fatigue test results shows, compares with as-welded, and the fatigue strength of T connector has improved 1.2 times.

Embodiment 2

Quench treatment process after the toe of weld TIG remelting of sheet material opposite joint.Material selection 16MnR low alloy steel (thickness 14mm), toe of weld TIG remelting and remelted layer Quench treatment process parameter are identical with embodiment 1.During the TIG remelting, the vertical test piece for welding of welding torch, arc axis is positioned at 0.5～1.0mm place, the toe of weld outside.The unrelieved stress test result is: under as-welded, and σ x=215MPa, σ y=164MPa; After the toe of weld TIG remelting, σ x=155MPa, σ y=129MPa; Spray is handled during toe of weld TIG remelting postcooling to 550 ℃, σ x=-209MPa, σ y=-198MPa.As seen, handle the back by this processing method and also be formed with the bi-directional compression stress field that is beneficial to raising fatigue strength in the toe zone.

Claims (1)

1.Q345 the method for steel toe of weld TIG remelting heel improving welded joint fatigue strength following chilling treatment is characterized in that step is:

(1) before the processing, removes lip-deep iron rust of toe of weld and splash earlier, clear up with grinder buffing;

(2) be that thermal source carries out remelting according to pre-set processing parameter along toe of weld with TIG electric arc, the angle between arc axis and the plummet is 0 °～30 °, and is positioned at 0.5mm～1.5mm place, the toe of weld outside;

(3) when toe of weld TIG reflow zone temperature was reduced to more than the critical temperature 100 ℃～200 ℃, water sprayed processing as low-temperature receiver to reflow zone, the temperature adjustment of TIG reflow zone when low-temperature receiver intensity is handled according to material, thickness of slab and Quench;

(4) after toe of weld TIG reflow zone Quench is handled, weldment is dried in case get rusty;

Q345 steel toe of weld TIG remelting processing parameter is: the tungsten electrode diameter: φ 3.2mm, and nozzle diameter: φ 12mm, shielding gas are argon gas; argon flow amount is 10～12L/min, and electric current is 170～180A, and voltage is 14～18V; speed is 13～16cm/min, and critical temperature is 450 ℃.

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