Key control points in industrial stainless steel casting processing: 7 technologies to solve the problems of porosity and shrinkage

In the production process of industrial-grade stainless steel castings, pores and shrinkage are common defects that affect product quality. These problems may lead to a decrease in the strength of the casting, failure of sealing or even direct scrapping. This article will systematically analyze the causes of defects and introduce 7 practical control technologies that have been verified by the industry.

1. Analysis of the causes of pores and shrinkage

1. Gas residue in the smelting process: If deoxidation is not sufficient during stainless steel smelting, hydrogen, nitrogen and other gases will precipitate during solidification to form pores.

2. Insufficient mold exhaust design: Improper setting of the exhaust channel of the resin sand mold or wax mold will hinder the gas discharge.

3. Gating system design flaws: Unreasonable gate position or cross-sectional area causes turbulent flow of molten metal into the air

4. Insufficient compensation for solidification shrinkage:Thick-walled parts are prone to shrinkage due to poor feeding channels.

2.7 key technical control points

1. Smelting process optimization

• Using Ar gas protection smelting to reduce hydrogen content

• Add rare earth elements (such as Ce) to refine the grains and reduce gas solubility

2. Mold exhaust system design

• Set up an exhaust groove with a cross-section greater than or equal to 6mm² on the parting surface

• Complex parts use 3D printed sand cores with built-in honeycomb ventilation structures

3. Stepped pouring scheme

• For castings with a height>500mm, a bottom pouring plus side pouring composite system is used

• The gate speed is controlled at 0.5-1.2m\/s (adjusted according to the wall thickness of the casting)

4. Directional solidification control

• Use chromite sand to make the riser, extending the feeding time by 30%-40%

• External cooling iron is installed in thick wall parts to force the establishment of sequential solidification gradient.

5. Process monitoring means

• Introducing an online detector for melt hydrogen content (control <>

• Using infrared thermal imaging camera to monitor mold temperature field distribution

6. Improvement of post-processing process

• Perform hot isostatic pressing (HIP) on pressure-bearing parts to eliminate internal micropores

• Add ultrasonic flaw detection and re-inspection after pickling

7. Material ratio adjustment

• For 316L austenitic steel, the Si content is controlled between 0.8% and 1.2% to improve fluidity.

• Add 0.03%-0.06% Ti element to fix free nitrogen

3. Comparison of typical cases

After a valve manufacturer implemented the above measures:

• The pore defect rate dropped from 8.7 percent to 1.2 percent

• Radiographic inspection pass rate increased to 98.5 percent (original 89.3 percent)

• 62 percent reduction in machining scrap costs