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Cause Analysis And Improvement Measures Of Stainless Steel 304 Wire Scale Defects Oct 11, 2017

Cause analysis and improvement measures of Stainless Steel 304 Wire scale defects

In view of the line scale defects on the surface of 304 stainless steel, the causes of the defects of the stainless steel surface are analyzed from the aspects of the shape and opening degree of the line scales. In the production of 304 stainless steel in practice, by improving the corrosion resistance of the stopper material, to ensure that the LF furnace soft stirring and sedation time, control the middle package tonnage and other related measures, stabilize the 304 stainless steel casting period plug bar opening degree changes, so as to achieve effective reduction of Stainless Steel 304 Wire scale defects.

Keywords: 304 stainless steel;

304 stainless steel is a nickel-containing austenitic stainless steel, belonging to Fe-cr-ni series alloy, is the main representative of austenitic stainless steel brand. Because 304 stainless steel cost advantage is insufficient, the market profitability is weak, in order to reduce the cost to enhance profitability, the company uses high sulphur phosphorus pig iron as 304 stainless steel smelting raw materials, because of its relatively low cost, that is called "low price nickel resources." With the large-scale use of low-cost nickel resources, under the existing raw material conditions, the original process technology has been unable to meet the user's product quality requirements, therefore, we must study the existing raw materials under the conditions of the process technology to meet the Low-cost and high-quality dual requirements.

In the production of 304 cold-rolled stainless steel plate, often on the surface of the strip appearance of line-like defects, called linear scale folding, referred to as "line scale." The defect of line scale is mainly distributed in the range of two lateral widths, which can only be observed after pickling of cold-rolled plate. Referring to the relevant effective measures adopted in domestic stainless steel production practice, and combining with the actual research results of the company, this paper synthetically analyzes the causes of the formation of line scale defects and adopts the corresponding control measures to reduce the defects of stainless steel surface quality.

1 304 stainless steel wire scale defect Introduction

The production process of two-step smelting 304 stainless steel in steelmaking plant of Baosteel Stainless steel company is as follows: Electric furnace →aod→lf→ continuous casting → slab grinding. The main processes for producing line scale defects are AOD, LF and continuous casting.

Stainless Steel 304 Wire scale defects are detected in cold rolled APC unit, the shape is small, the naked eye is not easy to observe, the length is about 20~80mm, the width is 0 5~1.0mm. This kind of defect can be found on the upper and lower surface of the steel coil, showing the characteristic of discontinuous and irregular distribution. Its morphological characteristics are shown in Fig. 1.

2 Genetic analysis

Speciation analysis of 2.1 Stainless Steel 304 Wire inclusions

2.1.1 Silicate inclusions

In this paper, the Energy spectrum analysis (Fig. 2) was made on the spot of 304 stainless steel coil, and found that there were two main types of inclusions in the defective parts.

A class of silicate inclusions containing Fe, Al, Si, Ca, Mg and other elements, this inclusions and slag composition is consistent, indicating that in the casting process there is slag involved in molten steel, molten steel casting slab, after cold rolling, the inclusion gradually close to the base surface, but not cracked outcrop, after grinding process, The surface of the substrate is damaged by the inclusion of the inclusions, and the defects of the line-like scales are presented.

2.1.2 $literal type inclusions

The energy spectrum analysis of 304 stainless steel coil at the site of the defect found that the defect site in addition to silicate inclusions, the others are mostly Al 2 o 3 inclusions, AL 2 o 3 is the most common oxide inclusions in the impact on the steel, a large number of Al 2 o 3 exist easy to form a blockage of the nozzle. During the casting, the blockage of the nozzle is expressed as the fluctuation of aperture in macroscopic.

Relationship between 2.2 line scale defect and aperture

The opening degree refers to the index of molten steel controlling the flow size of molten steel during casting. The fluctuation of the opening degree indicates that the control of the flow of molten steel is serious, the corrosion of the stopper can cause the spalling of the bar, resulting in the increase of the inclusions in the molten steel.

By doing the box-line diagram, it is found that there is a significant correlation between the aperture and the line scale defect. Figure 3 shows the opening and the line scale of the box line diagram, from the median value, the defect-free volume of the median value of 55.69, significantly higher than the line scale defect volume of 50.24. From the distribution interval, the aperture distribution of the line-scale defect volume is obviously lower than that of the defect-free volume.