Cause analysis of cracks in stainless steel bars

In the product application of stainless steel bars, sometimes affected by medium corrosion or external force, will form some cracks in the rod. This paper mainly talks about the causes of cracks in the stainless steel bar.

Bubbles in stainless steel bars

Cracks in 304 stainless steel bars are caused by bubbles on the surface of the skin or cracks on the surface. If the crack is perpendicular to the surface of the stainless steel and the length is about 0.8-1.5mm, there is no decarburization on both sides, which is caused by the bubbles under the skin. This is because there is a large amount of gas in the molten steel. When the molten steel is solidified, the gas is not discharged to form bubbles. The outer layer of the slab near the bubble is called subcutaneous bubbles, honeycomb shaped perpendicular to the surface of the billet, billet after rolling, it can weld most inside the bubble. But if the subcutaneous bubbles near the slab surface is too close, when heated due to slab surface oxidation or burning of the bubble surface will be exposed to the air bubbles in the oxidation, unable to weld, so that the stainless steel surface cracks.

Stainless steel is impure

Stainless steel six corner rod crack is caused by inclusions in stainless steel cracks, cracks and stainless steel surface forming a certain angle, length is about 1.0-2.5mm, slightly decarburization on both sides, decarburization layer 0.10-0.15mm. There are inclusions on both sides of the crack and the tail, and the ferrite bands are formed.

Stainless steel rod folding

Stainless steel square steel crack formation because of surface folding caused by the crack and the steel surface 15 -75 angle, the length of about 1.5-3.5mm, tail showing whirlpool, on both sides of slight decarburization, decarburized layer of 0.15 ~ 0.25mm, the crack in iron oxide existed. It is in the form of stainless steel rod surface along the direction of rolling straight or zigzag, continuous or discontinuous in partial or full length of steel. So it is known that this is the folding formed during the rolling of stainless steel.

The main reasons of the formation of folding is finished before the stainless steel rod rolling with a handleonapot; second is in the process of rolling each pass from the handle, flash, serious scratch, damage, and roll ring groove wear etc., will lead to product surface collapse; in addition a serious defect such as blank. If improper cleaning may also lead to finished folding.

So the main measures to reduce or prevent folding appear through the rational design of pass, the accurate estimation of the spread, precisely adjust the position of roller groove, reduce or eliminate the finished product before rolling the handle, flash, scratches and other defects; the second is to carefully clean the blank surface defects.

According to the causes of crack formation of stainless steel rod, can reduce or prevent crack using the following measures, one is to use the method of deoxidation alloying process is reasonable, appropriate control of oxygen content in molten steel, as far as possible to reduce the content of inclusions in molten steel; secondly, in the pouring process of pouring mining with full protection, to prevent the molten steel two oxidation, increase the purity of the billet, billet and reduce subcutaneous bubbles; the third is overheating degree of reasonable control of continuous casting steel, with excellent physical and chemical properties of slag, weak cold and ensure uniform cooling by two cooling, avoid the slab surface crack; the last method is through the rational design of pass, accurate estimation spread, precisely adjust the position of the roller grooves, carefully clean the blank surface to reduce or eliminate the serious defects before finished rolling handle, flash, scratches and other defects.

Source: China Stainless Steel Bars Manufacturer - Yaang Pipe Industry Co., Limited (www.yaang.com)