The Development of a Chromium – containing corrosion resisting steel

35 Years Ago

Extract from a paper presented at the Third South African Corrosion Conference, March 1980, by M.L. Melville, C.S. Mahony, J.P. Hoffman and K. Dewar, Southern Cross Steel.

Introduction

A new 12% Chromium steel, SX 3CR12, has been developed by Southern Cross Steel laboratories from AISI type 409.  It has improved toughness over AISI 430 and 409 in both the annealed and welded conditions.  A prototype field testing programme has been instituted and performance to date is discussed.

The prototype testing programme involves the controlled release of 3CR12 material for projects that have been investigated and considered suitable test applications.

Although a number of industries have been covered in the prototype test programme, the magnitude of gold and coal mining operations in South Africa, coupled with the enormous amount of material being consumed by corrosion and wear in these operations, make them ideal sites for testing of a corrosion resisting steel.  Earlier tests, using standard AISI 304 and 430 stainless steels, had shown that significantly improved performance could be obtained in applications such as ore hoppers and chutes.  3CR12, while being a significantly lower-priced material than 304 shows significant advantages over 430 in terms of toughness and weldability, while its corrosion resistance should be sufficient to make it suitable for these applications.

Four mining industry prototypes are described.

Headgear chute linerschute

The history of this particular shaft was that 25mm hard-faced mild steel plates were lasting approximately 5 weeks.  Wear plates of carbon manganese steel has also been tried but these were not cost effective.  In both instances ore build-up at the upper end of the chute necessitated weekly manual removal of this build-up.

A portion of the chute was lined with 3CR12 for test purposes. Immediate improvement was realized in that ore build-up was completely eliminated.  The most severely worn liner was removed after 5 months service and one plate lasted as long as 6,5 months.  This showed 3CR12 life to be at least 10 times that of hard-faced mild steel in this application.  3CR12 has been adopted as standard liner for this headgear chute, and tests in underground chutes and skips are being undertaken.

Surface ore car liners

Testing of 3CR12 in this application followed initial trials with 430. Previously, the 45 t cars in question were lined with 6 mm mild steel. These liners lasted 6-7 months in general.car liners

After 19 months, the 430 liners (6 mm) at the apex were replaced with 3CR12, and at this stage none of the 430 liners was less than 5 mm thick.  Lancing is not required to discharge the ore as slideability is far better.

In another car, half of the liners were of 430 and the other half of 3CR12.  The apex and door liners were increase to 10 mm thick.  After 6 months, wear was minimal and no difference was detected in either wear or discharge between the 3CR12 and 430 liner plates.  No maintenance had been required on the car.

Skip liners

Like headgear liners, skip liners are placed in wet abrasive conditions where extremely high wear rates are normal. 10 mm thick mild steel liners lasted 5-6 weeks in this application, which does not involve discharge problems. In the main impact area of the skip, 3CR12 lasted 2½ months, whilst it lasted 6 months in the rest of the skip.  Whilst these performances show some substantial improvement over mild steel results, trials are being conducted with alternative materials.

The test on skips suggest that 3CR12 may not be the ideal material for applications involving severe impact abrasion even when wet.  Severe dry abrasion is not an ideal application.

Transfer chute liner

At a colliery, the problems encountered with mild steel liners were corrosion, wear and sticking.  Liners of 8 mm thickness lasted 6-8 months.  3CR12 liner plate (8 mm) show no reduction in thickness after six months in service.